Downloaded audiobooks not transferring to BookPlayer app (iOS)

Apologize if this is not the right place to ask, but recently I’ve had multiple audiobooks that show up as 0s in BookPlayer when transferred from my files and do not play as a result. I uploaded the audio files to Dropbox, as suggested in the BookPlayer GitHub, and then shared to BP, but got the same result.

I’ve looked at the BP GitHub site for additional help, but still unable to find a solution. I’m not the most tech savvy, but am trying because it’s the best free iOS audiobook app I’ve found.

My guess is there is some sort of error in the downloaded mp3 files, but I don’t know how to convert or debug downloaded audio files on my phone.

Would really appreciate any guidance! Thanks in advance!!